Question

the fossil record shows that the average size of black bears was large during cold glacial periods and got smaller during warmer inter - periods. what is this an example of?
directional selection
disruptive selection
.ecosystem selection
stabilizing selection

Explanation:

• Directional selection: In directional selection, one extreme phenotype is favored over others. Here, during cold glacial periods, larger - sized black bears (one extreme) are favored (as they might have better heat - retention capabilities etc.), and during warmer periods, smaller - sized (another extreme) are favored. This shows a shift in the population towards one extreme phenotype in different environmental conditions.
• Disruptive selection: Disruptive selection favors both extreme phenotypes over the intermediate. But in this case, it's about one extreme at a time (large in cold, small in warm), not both extremes simultaneously.
• Ecosystem selection: This is not a standard term in evolutionary biology selection types.
• Stabilizing selection: Stabilizing selection favors the intermediate phenotype. But here, the phenotype is shifting towards extremes in different conditions.

Answer:

A. directional selection